The present invention generally relates to magnetic recording and/or reproducing apparatuses, and more particularly to a helical scan type magnetic recording and/or reproducing apparatus comprising a rotary drum which is mounted with rotary magnetic heads and a rotary erase head and is wrapped obliquely with a magnetic tape on an outer peripheral surface therof.
Presently, there are various types of helical scan type magnetic recording and/or reproducing apparatuses (hereinafter referred to as a video tape recorder or simply VTR) which record and/or reproduce signals on and/or from a magnetic tape. The VTR comprises a guide drum having a stationary drum and a rotary drum mounted with rotary magnetic heads, and the tape is wrapped obliquely around an outer peripheral surface of the guide drum for a predetermined angular range. The signals are recorded and/or reproduced on and/or from tracks on the moving tape by the rotary magnetic heads, where the tracks on the tape are formed obliquely to a longitudinal direction of the tape. As is well known, there are VTRs designed to operate in a normal speed mode and a long-time mode in which the tape is transported at a speed lower than that at the time of a normal speed mode so that the recording or reproduction can be carried out for a longer time by a given length of tape. Furthermore, there are VTRs having an editing function so that a new information can be inserted to replace an old information on a pre-recorded tape.
The VTR comprises a stationary full-width erase head which erases pre-recorded signals on the tape for the full width thereof. However, when carrying out an editing operation, the full-width erase cannot be used because the full-width erase head will erase portions on the pre-recorded tape which should not be erased. For this reason, a rotary erase head is provided on the rotary drum of the VTR having the editing function. When carrying out the editing operation, the rotary erase head scans the tracks to erase the pre-recorded old information therefrom and the following rotary magnetic head scans the erased track to record the new information thereon.
However, a track pitch of the tracks formed on the tape is different for the case where the tape is recorded in the normal speed mode and for the case where the tape is recorded in the long-time mode. In an example of a conventional VTR, the rotary erase head is mounted at a position equidistant from a pair of mutually confronting rotary magnetic heads on the rotary drum in a plan view of the rotary drum. Hence, in the case where the rotary erase head is mounted at a first height position so that it is possible to satisfactorily erase the information pre-recorded on certain tracks on the tape during the editing operation carried out in the normal speed mode of the VTR, it is possible to prevent the rotary erase head from scanning those tracks pre-recorded with information which should not be erased. However, when the diting operation is carried out in the long-time mode with the rotary erase head mounted at the first height position, the rotary erase head will erase a portion of a track which is pre-recorded with the information which should not be erased. On the other hand, in the case where the rotary erase head is mounted at a second height position so that it is possible to satisfactorily erase the information pre-recorded on certain tracks on the tape during the editing operation carried out in the long-time mode of the VTR, it is possible to prevent the rotary erase head from scanning those tracks pre-recorded with information which should not be erased. However, when the editing operation is carried out in the normal speed mode with the rotary erase head mounted at the second height position, the rotary erase head will erase a portion of a track which is pre-recorded with the information which should not be erased. For this reason, as will be described later on in the specification in conjunction with drawings, according to the conventional VTR, it is impossible to satisfactorily erase the pre-recorded information by the rotary erase head during the editing operation carried out in both the normal speed mode and the long-time mode.
It is possible to conceive such an arrangement that the height position of the rotary erase head is changed depending on the mode in which the editing operation is carried out, but this arrangement will suffer disadvantages such as complex construction and high cost.